People with hyperacusis are oversensitive to noises which others perceive as normal, for example traffic noise, cutlery on plates, dogs barking or doors slamming. Hyperacusis can affect those with hearing loss or normal hearing and those with tinnitus or Meniere's disease.

1. Aetiology in normal hearing

Normal perception of sound depends not only on detection and transmission from the cochlea via the auditory nerve to the auditory cortex, but also on auditory processing. Processing involves enhancement, amplification and suppression.

Sensory stimuli associated with a perceived threat (for example a bitter taste or touching a hot surface) provoke a dramatic response; similarly, threatening noise stimuli are perceived more acutely than background stimuli. They evoke an autonomic and emotional reaction appropriate to the 'fight or flight response' facilitating escape from predators.

In hyperacusis, non-threatening noise stimuli become subconsciously or consciously perceived as threatening or intrusive, or even painful; they can become associated with irritation, anger or frustration, or may provoke helplessness.

An analogy might be the anxiety triggered by entering a bus for someone who experiences panic attacks related to the use of public transport.

Misophonia is a dislike of a specific sound. The reaction to the sound is not a direct consequence of its volume but due to association and interpretation. This is evident because other pleasurable sounds can be tolerated at greater volumes. The intolerance worsens through emotional anticipation and autonomic reflexes (arousal, sweaty palms, agitation).

As with other phobias, a fear leads to a strongly held belief. The fear that the sound will cause damage to the ear is common in hyperacusis and often leads to a strongly held belief that the sound is harmful. The dislike of a specific sound may become extended to other sounds with a generalised fear of noise - phonophobia - regardless of volume.1

Anxiety and fear may lead to avoidance behaviours: seeking out silence using 'attenuators', such as earplugs.

This paradoxically can exacerbate the problem as the auditory processing adapts to the reduced input.

Some patients without tinnitus may develop the belief that hyperacusis may result in tinnitus and so develop avoidance behaviours.

2. Hyperacusis with hearing loss

In some people with hearing loss (usually high frequency) a disproportionate number of nerve cells may be stimulated by sounds at frequencies which the person can still detect. This 'recruitment' means that noise stimuli are perceived as louder and/or distorted.

Optimising hearing with hearing aids levels out the contrast between the offending sounds by improving the hearing of background noise and so helps hyperacusis.

3. Treatment and research

Hearing therapists are skilled at explaining hyperacusis and use counselling, auditory desensitisation and retraining.

Enrichment of background sound with or without wearable sound generators may be used.

CBT techniques may be used with misophonia or phonophobia. A behaviour modification programme with a clinical psychologist is effective.

MRI studies of those with hyperacusis show increased activity in the midbrain, thalamus and primary auditory cortex compared with people with normal noise tolerance. Patients with tinnitus similarly have increased activity in the primary auditory cortex compared with controls. Comparisons with chronic neuropathic pain and photophobia have been made.2

In some migraine sufferers there is a correlation between cutaneous allodynia and hyperacusis.3 Hyperacusis has been noted as a symptom in patients with semantic dementia,4 and cases of hyperacusis as a presenting symptom of MS have been reported.5

Be aware of hyperacusis and ask about it when patients have hearing loss, tinnitus or Meniere's disease.6

Be aware of hyperacusis as a symptom in migraine, dementia and post-concussion syndrome.

Ask about triggers, for example history of loud noise exposure or head injury. Ask about symptoms of migraine.

Offer reliable information about hyperacusis (see Resources).

Reassure that normal noise is not damaging in hyperacusis.

Refer for a hearing test to identify (and treat) any hearing loss; audiometry can identify the level at which discomfort develops; an ENT consultant specialising in audiology can refer to a hearing therapist.

Teach some simple relaxation techniques or recommend a local class.

Diagnose and treat any coexisting anxiety or depression (PHQ9 and GAD7 questionnaires).

Be empathetic and positive about the prognosis.

Explain that using earplugs and seeking silence may exacerbate the problem and that specialist hearing therapy guided desensitisation is very effective; prepare the patient for the fact that this is a gradual process, which may take up to 12 months.

Offer to explain the condition and treatments to the family.

Preserve hearing – consider occupational factors where there is hearing loss and encourage use of ear protection if there is exposure to loud noise at work.